This invention relates to an improved AC memory driving type self-shift type gas discharge panel. It more specifically relates to a new type panel structure which can suppress accidental abnormal discharges caused by deviated abnormal charges.
The self-shift type gas discharge panel is classified as an AC memory driving type plasma display and provides means to directly shift the information written in the form of a pattern of discharge spots at one end of the panel, with the pattern being unchanged during the shift in order to obtain a stationary display at a predetermined position. The electrodes of such a panel are covered with a dielectric layer in order to attain the memory function. Presently, the panel with such a structure has the problem of undesirable generation of abnormal discharges during operation, which causes a disturbance in the displayed information in the panel, and breakdown of the dielectric layer.
The abnormal discharge appears, for instance, around the discharge spot group corresponding to the displayed information in the form of unit discharge spots, or it appears as a comparatively large light emitting pattern after a momentary emission of light resembling a spark.
Such an undesirable abnormal discharge is particularly significant when the so-called wall charge transfer system is employed as the drive method, in which a combination of wall charges is used for the shift operation as described in U.S. Pat. No. 3,781,600 by Coleman et al. It is also significant when the drive method of the so-called space charge coupling system is employed, in which the coupling of space charge is used for the shift operation as described in U.S. Pat. No. 4,132,924 by Yamaguchi et al. Therefore, the cause is considered to be that abnormal charges are accumulated in a polarized condition at the surface of the dielectric layer corresponding to the electrodes at both ends of a shift channel due to the repeated shift operation. FIG. 1 shows schematically the deviation of such abnormal charges. In this figure, the horizontal axis indicates the shift channel with the right side being the end for writing in information, while the vertical axis shows the resulting voltage. Such a deviated wall charge becomes significant due to the repeated shift operation, and when it exceeds a certain value an abnormal field based on this abnormal wall charge induces an avalanche phenomenon in the vicinity of the abnormal wall charge, often in combination with an external field such as the shift voltages, and thereby an abnormal discharge occurs which is not based on the data, as explained above.
It is known to provide electrodes for dissipating the abnormally accumulated charge at both ends of the shift channel in order to avoid such abnormal discharges. For example, the gas discharge panel of the type of the above-cited U.S. Pat. No. 3,781,600 employs a structure in which the accumulation of charges is prevented by directly exposing electrodes at both ends of the shift channel in the gas discharge space. However, use of exposed electrodes as explained above causes the electrode material to sputter due to ion impacts during discharge, or causes oxidation of the electrodes during the baking process for the sealing material when sealing the panel. At any rate, employment of such exposed electrodes has the disadvantage that the operating lift is curtailed due to a change of the discharge characteristics at the area near the pertinent electrodes. In addition, it is also a problem that the upper limit of the write voltage margin is lowered. Namely, when the write voltage is applied to the exposed write electrodes, a heavy current flows for a comparatively long period, and therefore an intensive discharge continues for this long period at the write discharge cells defined by the write electrodes, which causes an unwanted discharge at the adjacent shift discharge cells. Consequently, it is necessary to keep the upper limit of said write voltage to a lower value.
On the other hand, U.S. patent application Ser. No. 213,464, entitled "Self-Shift Type Gas Discharge Panel" by Shinoda et al, assigned to the same assignee as the assignee of the present invention, proposes a structure in which a pinhole or crevice is provided for dissipating the charges on the dielectric layer in the vicinity of the electrodes at both ends of the shift channel. However, such a charge dissipation structure brings about problems, for instance, it is difficult to form this panel having homogeneous characteristics with excellent reproduceability, and also in this case, the electrodes are oxidized due to the existence of the pinhole or crevice.